Thixotropic agents find usage in a wide variety of applications stretching from food preparation to use in downhole fluids used in the drilling, completing and production of oil and gas wells. In particular, and with respect to the oil and gas industry, hydraulic fracturing of downhole formations for enhanced recovery techniques is rising dramatically. As is well known, in the United States there are numerous shale formations containing trillions of cubic feet of natural gas and billions of barrels of oil. The problem with these shale formations is that the oil and/or gas is tightly held because of the generally small pore size of the shale. Accordingly, unlike in other formations, the oil and gas is not readily released from the formation for production. To overcome this difficulty, operators have resorted to hydraulic fracturing or “fracking.”
In fracking, the fluid, e.g., a liquid, gas or two-phase fluid, is injected into a downhole formation at sufficient pressure and flow rate to fracture the subterranean formation. Typically, a proppant material such as sand, fine gravel, sintered bauxite, glass beads or the like can be introduced into the fractures to keep them open, i.e., propped. These propped fractures provide larger flow channels through which an increased quantity of hydrocarbon can flow, thereby increasing the production capability of a well.
It is known to use hydrophilic materials, sometimes referred to as “gelling agents” to increase the viscosity of the liquid fracturing fluids. These high viscosity aqueous fracturing fluids lead to the development of wider fractures to improve productivity further into the formations, increase the proppant carrying capacity of the fracking fluid, and permit better fluid loss control.
Additionally, high viscosity treating fluids are used for carrying out subterranean well completions, for transporting sand in sand and gravel packing procedures and in various other well treating procedures. Further, high viscosity treating fluids have the ability in cleaning applications such as in the cleaning of tubular goods, production equipment and industrial equipment.
Hydrophilic gelling agents such as partially hydrolyzed polyacrylamides, natural gums, modified natural gums, celluloses and xantham polymers have been utilized in the past to increase the viscosity of aqueous media. However, in many cases, the gels produced with these gelling agents have limited stability at elevated temperatures, i.e., the viscosity of the gel in aqueous solution decreases substantially after only a short period of time. On the other hand, chemicals which cross-link complex hydrated gelling agents have also been utilized for further increasing their viscosity, see for example U.S. Pat. Nos. 3,888,312; 4,021,355; 4,033,415; 3,959,003; 3,979,303; 4,413,834; 4,324,668; and 4,579,670.